The prior art has prepared filaments from pitch based (petroleum and/or coal tar) compositions by the conventional technique of melt spinning into fibers or filaments which can be converted into multi-filament assemblies and thereafter oxidatively stabilized. Such fibers or assemblies are taught to be useful per se or the filaments or assembly of filaments may be chopped or the fibers may be stretch broken into what the art refers to as a "staple" fiber. Such "staple" thereafter may be converted by drafting, drawing and/or twisting, referred to as spinning in the industry, the chopped filaments (staple fibers) into a yarn. The continuous filaments are made into tows formed from a plurality of the continuous mono-filaments. The resulting yarns or threads are used per se or may be woven into cloth-like articles and used as such. Alternatively, a woven cloth-like article may be carbonized to produce a graphite or graphite-like cloth. In addition, a fiber tow per se, without weaving, may be carbonized and thereafter used as a reinforcement material for synthetic resinous materials e.g., "pre-preg", and the like.
In a somewhat similar manner polyacrylonitrile has been wet spun into filaments, assembled into filament tows, stabilized by oxidation and the tows made into staple by chopping or stretch breaking. The staple is then spun into yarn, the yarn is knit or woven into a cloth or fabric, and, if desired, the resulting fabric carbonized at a temperature of greater than 1400 degrees. These materials, in their precarbonized woven state, have been used as non-combustible reinforcing materials for metallized fire fighting suits. These materials, in their unwoven carbonized form, have been used as a reinforcement material for synthetic resinous composites.
In preparing uncarbonized conventional polymeric textile yarns for knitting, weaving or other textile manufacture it is the usual practice in the industry to pinch crimp the yarn and thus crimp-set the individual fibers of the yarn (placing sharp acute bends in the fiber). Such textile treatment methods provide the same effect if used on a carbonaceous yarn, i.e., severe sharp crimps are applied to the yarn causing entanglement among the individual fibers of the yarn and thus assisting in maintaining or fixing the fibers in the yarn as well as to impart bulk properties to the yarn. However, when the procedure for the manufacture of ordinary textile yarn is followed and a carbonizable precursor yarn is crimped then carbonized, usually at a temperature above about 1000 degrees C. and more practically at temperatures of 1400 degrees C. and above, the resulting yarn (the filaments and/or fibers) becomes very brittle. That is to say, the yarn cannot be harshly handled or sharply creased, unwoven, garnetted, deknitted or carded without breaking the fibers in the yarn into small segments. As a result of such brittleness, a knitted fabric cannot be deknitted without special care and such deknitted yarn cannot be carded to convert the fibers in the yarn into a wool-like fluff without causing a severe destruction, i.e. breakage, of the fibers.
The prior art generally discloses linear carbonaceous filaments having a high tensile strength or a high surface area. The manufacture of such filaments of alleged "graphitic" nature have necessitated the utilization of high temperatures to obtain a high degree of carbonization. However, the filaments produced from such a high temperature treatment are very brittle and incapable of standing up to stress such as a repeated bending of the filaments, particularly when they have been subjected to a temperature above about 1000 degrees C. particularly at about 1400 degrees C. Exemplary of a high temperature treatment of filaments derived from stabilized mesophase pitch is found in U.S. Pat. No. 4,005,183 where the fibers are stabilized and made into a yarn having a low (below normal absorptive carbon) surface area and a Young's modulus within the range of from 1 to 55 million psi.
Another technique for making a fabric panel is described in U.S. Pat. No. 4,341,830 in which a tow of acrylic filaments is oxidized under tension, at a temperature of from 200 degrees to 300 degrees C., crimped in a stuffer box, made into staple fibers and spun into a yarn which is then knitted into a cloth panel and heat treated, i.e. carbonized, in an inert atmosphere at a temperature of up to 1400 degrees C. The so carbonized cloth panels are assembled into a stack and the stack placed into a carbon vapor furnace for deposition of carbon onto and into the stack. This treatment is carried out by passing a carbonaceous gas, methane, through the stack while inductively heating the stack to 2000 degrees C. to cause carbon to be deposited onto and into the stack and produce a carbonaceous body having a matrix of panels. The yarn made by this process has been found to be very brittle, and cannot be subjected to repeated acute angle stress bending, as would occur if the cloth panel were deknitted, without a severe breakage of the fibers in the cloth.
U.S. Pat. No. 4,193,252 to Sheppherd, et al discloses the making of partially carbonized, graphite and carbon fibers from rayon which have been knitted into a carbon assembly. When the fabric is deknitted, the partially carbonized and the carbonized fibers contain kinks. The fully carbonized or graphite fibers have kinks which are more permanent in nature. Applicants have found that partially carbonized rayon fibers are flammable, do not retain their reversible deflection and lose their kinds at relatively low temperatures or under tension. The fully carbonized or graphite yarn which is prepared from rayon is brittle and difficult to handle when deknitting. Moreover, carbon fibers produced from rayon are known to posses higher water absorption and their tendency to recover from compression is poor. If a mat of these fibers is laid down and thereafter placed under a compressive force, the mat will not re-expand to its original loft.
The term "stabilized" herein applies to fibers or tows which have been oxidized at a specific temperature, typically less than about 250 degrees C. for PAN fibers, provided it is understood that in some instances the filament and or fibers are oxidized by chemical oxidants at lower temperatures.
The term "Reversible Deflection" or "Working Deflection" is used herein as it applies to a helical or sinusoidal compression spring. Particular reference is made to the publication "Mechanical Design - Theory and Practice", MacMillan Publ. Co., 1975, pp 719 to 748; particularly Section 14-2 pages 721-24.